Content may be transmitted by a geosynchronous satellite communication network to users for decoding and playback. A system diagram of a typical satellite download link is illustrated in FIG. 1. The satellite downlink 100 includes a satellite antenna 102 connected to a low noise block converter (LNB) 104. The LNB is connected to a satellite receiver/decoder 106. The satellite can transmit signals including content channels modulated on a carrier. The content channels can be analog content channels or digital content channels. In many systems, data is modulated onto the same carrier using different polarizations. Where digital content channels are modulated onto a carrier, the digital data modulated on the carrier can include a plurality of digital content channels, each of which typically includes at least one video and/or audio stream.
In many instances, a signal containing multiple content channels is transmitted to a satellite network from an uplink facility. A transponder on the satellite then transmits a signal that can be received by a number of satellite antennas 102. The received signal is then passed to a LNB 104, which down converts the signal to an intermediate frequency (IF). Lastly, the IF signal is passed to a satellite receiver/decoder 106, such as a set top box, where the signal containing content is demodulated and decoded (i.e. audio and/or video) for playback.
In this way, information transmitted as relatively high frequency satellite signals, usually as microwave signals, may be converted to similar signals at a much lower frequency, usually known as an intermediate frequency (IF) compatible with the electronics of the decoding device and/or cabling used to connect an LNB to a satellite receiver/decoder. A content channel is the digital data modulated onto a carrier frequency within the IF signal. Users may then receive selected content channels as IF signals for decoding and use. Representations of the frequency spectra of signals during various stages in the down-conversion of satellite communication signals is illustrated FIGS. 2A, 2B and 2C.
Radio frequency (RF) signals are typically transmitted by a satellite to a receiver at high frequencies. A typical satellite radio frequency (RF) signal for downlinking is illustrated in FIG. 2A. As illustrated, the signal is transmitted at high frequencies, spanning from 11 GHz to 12 GHz. A satellite signal when received by a satellite signal receiver is usually weak after traveling great distances during transmission and is of a relatively high frequency. When signals are sent through coaxial cables, the higher the frequency, the greater the losses that occur in the cable per unit of length.
A LNB may be used to amplify and convert these high frequency signals to a lower, more manageable frequency. The frequency spectrum of satellite signals processed by a LNB is illustrated in FIGS. 2B and 2C. In Europe, the standard is often horizontal polarization and vertical polarization. In the U.S., the standard is often left circular and right circular polarization. The frequency band for each polarization is 10.7-12.75 GHz. The total bandwidth received at a satellite antenna is typically greater than 4 GHz. The frequency band for satellite signal transmission in a coaxial cable is 950-2150 MHz. In Europe, the frequency spectrum of LNB processed signals may be from 950 MHz to 2150 MHz (see FIG. 2B). In the United States (U.S.), the frequency spectrum of LNB processed signals may be from 950 MHz to 1450 MHz (see FIG. 2C).
Signals containing content received from a satellite typically include multiple content channels in the frequency band of the carrier signal. Typical frequency spectrum for carrier frequencies of channels of encoded digital data carried by the IF signal processed by a typical LNB is illustrated in FIG. 2D. An LNB can separate the 4 GHz bandwidth into smaller bandwidth signals that are sent out instead of the full band. Here, the frequency band spans from 950 MHz to 2150 MHz or 1450 MHz and there are multiple 36/55 MHz content channels in this frequency band. In order for a user to decode selected content, an L-band tuner may be used to select the desired channel. For example, a certain carrier frequency may be selected where a 36/55 MHz band may be transferred to a decoding device for use by the user.
LNBs can be implemented in many ways using many different LNB architectures. FIG. 3 illustrates a diagram of a typical universal LNB architecture with dual outputs. In this architecture, the LNB receives two RF input signals from the satellite. One signal is for the vertical polarization antenna 302 and the other is for the horizontal polarization antenna 304. For example, the frequency band of both signals may be from 10.7-12.75 GHz. The LNB first separates the signal into two bands with two band pass filters, a low band 306 (10.7-11.7 GHz) and a high band 308 (11.7-12.75 GHz). Low band signals are mixed down to 950-1950 MHz with local oscillator (LO) 310 at 9.75 GHz. The LO is the frequency used in the LNB to block convert the frequency of the satellite signal, or transponder frequency, to a lower frequency band. High band signals are mixed down to 1100-2150 MHz with LO 312 at 10.6 GHz. Output signals are selected from the four down converted L-band signals with a 4:2 multiplexer 314 in response to request for specific channels from the decode device. Using the Universal LNB illustrated in FIG. 3, viewers can only tune to content on two of the 1 GHz L-band channels at any time. Additional cables are required for users to watch content from more than two of the 1 GHz L-band channels.
Instead of utilizing multiple cables, however, coax cable can be replaced with optical cable. Optical cable is able to carry the full 4 GHz bandwidth (or even greater bandwidth in systems that receive signals from multiple satellite transponders). In order to use optical cable, an optical LNB can be utilized. Optical cable installation is also beneficial in buildings where no exiting cable television (CATV) cable is present. FIG. 4 illustrates a block diagram of a typical optical LNB. In the illustrated optical LNB architecture, the optical LNB receives 2 RF inputs. One is from the vertical polarization antenna 402 and the other is from the horizontal polarization antenna 404. In many instances, the frequency band of both signals is 10.7-12.75 GHz. The vertical polarized signal is mixed down to 0.95-3 GHz with a LO 406 at 9.75 GHz. The horizontal polarized signal is mixed down to 3.4-5.45 GHz with a LO 408 at 16.15 GHz. The two mixed down signals are combined into a single signal (412) and converted to an optical signal via an optical driver 414 and output through an optical cable 410. The output frequency for an optical LNB as illustrated here may be 0.95-5.45 GHz.
Typically, satellite set top boxes (STB) are configured to receive L-band RF signals at 950-2150 MHz. In order to interface with a satellite STB, an optical converter is used for each STB to convert the optical signal back to an RF signal. FIG. 5 illustrates a typical block diagram of an optical converter 502 at the STB side for converting an optical signal to a RF signal. The function of the optical converter is to convert the optical signal into a RF signal and to mix at least a portion of the RF signal to the L-band, for example at 950-2150 MHz. FIG. 6 shows a block diagram of a typical optical converter at the STB side. In this optical converter architecture, the optical signal received from the optical cable 608 is converted to a RF signal using a photo detector (PD) 602. The full four GHz band is separated into four one GHz signals with four band-pass filters 604. Each filtered signal is frequency translated to the L-band, with a mixer if necessary. The final output is selected between these four L-band signals with a multiplexer (Mux Sell 606.
In the system illustrated in FIG. 6, to select frequency band 1950-3000 MHz, the RF signal is first filtered by a band-pass filter 610 for 1950-3000 MHz. The filtered signal is then mixed down 1100-2150 MHz with LO 612 at 4.1 GHz. The multiplexer (Mux Sell then selects the content channel associated with the signal at frequency band 1950-3000 MHz.